Presence-sensitive displays such as touchscreen displays are able to detect a presence or a touch within the active area typically overlaying a display, such as detecting whether a finger is present pressing a fixed-image touchscreen button or detecting the presence and position of a finger. Some presence-sensitive displays can also detect the presence of elements other than a finger, such as a stylus used to generate a digital signature, select objects, or perform other functions.
Use of a presence-sensitive display allows an electronic device to change a display image, and to present different buttons, images, or other regions that can be selected, manipulated, or actuated by touch. Presence-sensitive displays such as touchscreens can therefore provide an effective user interface for cell phones, Global Positioning System (GPS) devices, personal digital assistants (PDAs), computers, Automated Teller Machines (ATMs), and other devices.
Presence-sensitive displays use various technologies to sense touch from a finger or stylus, such as resistive, capacitive, infrared, and acoustic sensors. Resistive sensors rely on touch to cause two resistive elements overlapping the display to contact one another completing a resistive circuit, while capacitive sensors rely on the presence of a finger changing the capacitance detected by an array of elements overlaying the display device. Infrared and acoustic touchscreens similarly rely on a finger or stylus to interrupt infrared or acoustic waves across the screen, indicating the presence and position of a touch.
Capacitive and resistive touchscreens often use transparent conductors such as Indium tin oxide (ITO) or transparent conductive polymers such as PEDOT to form an array over the display image, so that the display image can be seen through the conductive elements used to sense touch. The size, shape, and patter of circuitry have an effect on the resolution and accuracy of the touchscreen, as well as on the visibility of the circuitry overlaying the display. Other materials, such as fine line metal elements are not optically transparent but rely on their small physical width to avoid being seen by a user.
One common application for presence-sensitive displays is presentation of keyboards, numeric keypads, and other input displays on mobile devices such as cellular telephones or “smart” phones. Presence-sensitive displays can also enable a user to provide input by drawing shapes or making gestures, such as by pinching in or out on a displayed object to perform a zoom, or by drawing a graphical object. But, drawing shapes with a finger can be imprecise and slow, and it is therefore desirable to facilitate better touchscreen input using such methods.